1. Field of the Invention
This invention relates generally to a method and apparatus for controlling an internal combustion engine and more particularly to a microprocessor-based electronic engine control system having a memory preprogrammed with various control laws and control schedules responsive to one or more sensed engine-operating parameters for computing command signals for controlling fuel injection, ignition timing, EGR control, or the like.
2. Statement of the Prior Art
Many of the patents of the prior art recognize the need for employing the enhanced accuracy of digital control systems for more accurately controlling one or more functions of an internal combustion engine.
U.S. Pat. No. 3,969,614 which issued to David F. Moyer, et al on July 13, 1976 is typical of such systems as are U.S. Pat. No. 3,835,819 which issued to Robert L. Anderson, Jr. on Sept. 17, 1974; U.S. Pat. No. 3,904,856 which issued to Louis Monpetit on Sept. 9, 1975; and U.S. Pat. No. 3,906,207 which issued to Jean-Pierre Rivere, et al on Sept. 16, 1975. All of these patents represent a break-away from the purely analog control systems of the past, but neither the accuracy, reliability, or number of functions controlled is sufficient to meet present day requirements.
Future internal combustion engines will require that emissions be tightly controlled due to ever-increasing governmental regulation, while fuel consumption is minimized and drivability improved over the entire operating range of the engine. None of the systems of the prior art provide a method and apparatus for controlling the operation of an internal combustion engine over its entire operating range with sufficient accuracy to attain minimal emissions and minimal fuel consumption together with improved drivability.
The systems prior art attempt to control one or more of the engine-operating functions but none attempts to control the operation of the fuel pump, fuel injection, engine ignition timing, on-off and/or proportional EGR control, and the like while using feedback from such devices as oxygen sensors for emission control purposes or for effecting a closed loop fuel control operations, while yet further including provisions for optimizing acceleration enrichment handling, and the like. Moreover, the systems of the prior art are extremely expensive, often too large to install, difficult to repair and maintain and are, therefore, not commercially feasible at the present time.
These and other problems of the prior art are at least partially solved by the Applicant's improvements in microprocessor-based electronic engine control systems which enable the improved systems to eliminate most or all of the problems of the prior art. The improvements set forth herein enable the implementation of a microprocessor-based electronic engine control system capable of executing much more advanced and complex fuel control laws than heretofore achievable in the prior art and enable the engine control system to expand the number of control functions performed thereby while, at the same time, reducing the cost and size of the unit and increasing reliability so as to render the system commercially feasible.
The analog-to-digital conversion circuitry with window counter and feedback compensation is a highly efficient low cost means for implementing the required A/D conversion while greatly increasing the accuracy of the conversion over any of the systems of the prior art. The oxygen feedback sampler described herein avoids the problems inherent in the prior art such as a loss of accuracy due to invalid signals from cold sensors. The system of the present invention avoids the problems of the prior art and provides a greatly improved method and apparatus for sampling oxygen sensors wherein, the sensors are sampled at a rate which changes as the engine speed changes and the samples are taken periodically at a rate sufficient to enable the sampling to always be accomplished in one revolution or less.
Furthermore, the prior art teaches many highly inaccurate methods for controlling ignition timing and most of these systems prove totally unreliable when the engine is in a "cranking" mode operation. The ignition timing system of the present invention avoids the problems of the prior art by controlling the timing of firing pulses to the spark plugs by generating two separate programgenerated ignition control words. One control word may be used to calculate an ignition delay from the occurrance of an engine position pulse until the time of the spark and the second word controls the ignition pulse-width thereby determining the duration of the spark. A solution to the unreliability problem during the "cranking mode" of operation is also included herein.
These and other objects and advantages of the present invention will be accomplished by the method and apparatus of the present invention which cooperate to produce an improved engine control system far superior to any heretofore known in the prior art.